The present invention relates to a process for producing tube containers by molding a container mouth section of resin (e.g., plastic) and fixing it onto one end of a tube, and to a molding apparatus for manufacturing the same.
FIG. 17 shows a sectional view of a conventional tube container 80.
The tube container 80 is formed by molding a container mouth section 82 of resin and fixing it to one end of a tube 81 made of laminated metallic foil and plastic sheets.
In using the tube container 80, a suitable cap is applied on the container mouth section, and a pasty content such as dentifrice, mustard, or wasabi (i.e., Japanese horseradish) is introduced into the container. Finally, the bottom section is sealed.
The tube container 80 is formed by molding and fixing the container mouth section to a previously formed tube 81.
Conventionally, the formation of the container mouth section 82 on the tube has been effected exclusively by compression molding.
FIGS. 18-20 illustrate the sequence of the conventional compression molding system.
First, as shown in FIG. 18, a tube 81 is inserted onto the core 84 of a core mold 83 and fixed there.
Next, a split mold 85 is closed causing the forward end edge of the tube 81 to be bent slightly inward. A resin melt is introduced into the cavity within the split mold 85, and a movable mold 86 is applied to compress the resin melt into the container mouth section (FIG. 19). Finally, the mold assembly is disassembled to take out the tube container thus formed (FIG. 20). The reason why the forward edge of the tube 81 is bent slightly inward is to increase the bonding strength between the tube 81 and the container mouth section 82.
The above-described conventional tube-container manufacturing apparatus involves a number of problems as follows:
(1) Simultaneous multiple manufacture is difficult, thus productivity cannot be increased.
(2) The split mold 85, when closed to form the bent section, may pinch the tube 81. In such a case, the tube 81 is deformed and the incomplete closure of the split mold 85 causes the resin melt to leak out whereby inferior products are produced.
(3) In the compression mold as already described, resin melt is introduced into the open cavity of the core mold where it is compressed merely by the movable mold 86. Thus, the molding pressure in itself cannot be effectively raised. Such a low pressure is apt to result in unequal pressure exerted on the resin melt inside the cavity and in the sink mark in the shoulder of the container mouth section 82, etc., which inevitably leads to low dimensional precision. Therefore, container mouth sections of complex shape are very hard to manufacture through molding.
(4) It is difficult to introduce a predetermined amount of resin melt into the cavity, which results in dimensional errors in the molded products.
(5) For the main reasons that no prescribed amount of resin melt can be introduced and that the mold assembling pressure is low, molded products tend to have flashes which necessitate an extra deflashing process.